Wireless devices for communication such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two wireless devices, between a wireless device and a regular telephone and/or between a wireless device and a server, such as server providing video streaming service, via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, computers, or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
A cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNodeB (eNB), NodeB, B node, Base Transceiver Station (BTS), or AP (Access Point), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the wireless devices within range of the base stations also referred to as transmitter-receiver pairs. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to a wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for terminals. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE is controlled by the radio base station.
Dynamic Adaptive Streaming over HTTP (DASH), also known as Moving Picture Experts Group (MPEG)-DASH, has been adopted by 3GPP targeting to unify behaviors of different adaptive streaming video services and vendors. HTTP is the abbreviation for Hypertext Transfer Protocol. A general mobile network media flow of DASH, or any other HTTP Adaptive Streaming (HAS) video solution in a mobile network is exemplified in FIG. 1. The video server may be incorporated in normal web servers with storage of video representation with different codec rates. The client e.g. in a wireless device sends a first video request with an initial rate, typically a low rate to a video server, followed by a bundle of video frames comprising video data transmitted from the media server also referred to as a video server. The bundle of video frames, also called video segment, is composed of the subsequent frames in an interval of several seconds.
It is typically the client that performs the bit rate adaptation to match an estimated available network bandwidth also sometimes referred to as estimated throughput. The client bit rate adaptation has the benefit that the client may directly keep track of the variation of the downloading rate and the playback buffer. The rate adaptation may be triggered for each video segment hence the size of the video segments influences the frequency of the rate adaptation. A requested video clip starts to play when a given level of the playback buffer is filled. The playback is frozen if the buffer is underrun, i.e. empty, and re-started when enough pending video is received this is referred to as re-buffering.
A utility maximization problem that separately takes into account different utility functions for HAS video and data flows have been discussed. This showed that the utility maximization may be achieved through an algorithm, Adaptive Guaranteed Bit Rate (AGBR), wherein target bit rates are calculated for each HAS flow and passed on to an underlying minimum rate proportional fair scheduler that schedules resources across all the flows.
In “Improving Fairness for Adaptive http video Streaming” by B. Villa et al, an analysis of a suggested method for improving fairness among competing adaptive video streams is provided. The metrics used as fairness indicators are differences in achieved average rate and stability among the competing streams. The method analyzed is based on changing a fixed and equal video segment request rate (T) of each stream, to either a per session unique or random request rate.
This scheme is helpful for distributing to video users in time by having different segment request rates, and therefore may give a positive impact on the utilization of a link, and help the video users. However, it does not work so well in high load situations.
Streaming video over mobile networks, such as LTE, is increasing and more content providers are appearing on the market. Dynamic Adaptive Streaming over HTTP is one standardized solution for providing rate adaptive video streaming. One problem that users watching video are experience is buffer underrun which causes the video playback to freeze. Another problem is that the streaming video users are taking too much of the shared resources from other data applications, i.e. there is an unfair situation that may occur. This depends on the type of congestion control algorithms in the streaming video and the other data servers, and how the transmission network is configured to treat the different flows.
Network assisted rate adaptation, may optimize the issue of fairness between the video clients and between video and other traffic, especially in the RAN, which has been observed in existing research activities. However, the improved rate adaptation can only operate in the typical time unit of seconds, depending on the size of the video bundle which includes a couple of consecutive video frames, which are also called video segment or video chunks. The radio schedulers in 3rd Generation (3G) and 4th Generation (4G) mobile systems operate on a few milliseconds basis with, in case of a proportional fair scheduler, typically a fairness consideration based on transmitted bits and channel quality in the order of a few seconds. These two functions separately only solve parts of the problems of buffer underrun and unfairness.
An update frequency of the target bit rate is dependent on the playback time that the video segment consist of as it is the video client that request a new segment and the state of the art clients request the new segment when one or several segments has been played. This gives the characteristics of the pending video as in FIG. 2 where a request is triggered when the pending video in the play-out buffer is 30 s. FIG. 2 depicts an example of amount of pending video in the play-out buffer with respect to time.